The present invention is directed to a point-to-multipoint digital communications system. More particularly, the present invention is directed to a point-to-multipoint communication system that facilitates use of a reduced complexity receiver architecture at the multipoint sites.
Point-to-multipoint communications systems having a primary site that is coupled for communication with a plurality of secondary sites are known. Generally stated, such systems comprise a head end unit comprising a transceiver at a primary site that functions as a central communications device for communication with a plurality of transceivers at a plurality of secondary sites.
One application of such a communications system type is a cable telephony system. Cable telephony systems transmit and receive telephone call communications over the same cable transmission media as used to receive cable television signals and other cable services. One cable telephony system currently deployed and in commercial use is the Cablespan 2300 system available from Tellabs, Inc. The Cablespan 2300 system uses a head end unit that includes a primary transmitter and primary receiver disposed at a primary site. The head end unit transmits and receives telephony data to and from a plurality of remote service units that are located at respective secondary sites. This communication scheme uses TDM QPSK modulation for the data communications and can accommodate approximately thirty phone calls within the 1.9 MHz bandwidth typically allocated for such communications.
Generally, each receiver of each remote service unit receives a burst of continuous, sequential data symbols during a single, predetermined time slot occurring in each frame of data sent by the head end unit. As such, the receiver must have enough processing power to process the burst as it is received during the short burst period of each frame. Such processing power results in increased costs of the remote service units. While small point-to-multipoint systems may be able to tolerate these increased costs, the increased costs may make large scale systems uneconomical and unfeasible.
The present inventors, however, have recognized that such burst processing may be wasteful and require an undue amount of processing power. To this end, they have devised a system in which the processing power for each of the remote receivers may be substantially reduced.